Device and method for coupled measurements for globally and continuously tracking traces of tars present in a gas flow

Abstract

The measurement is carried out by a device of two non- dissociable measurement chains resulting in a continuous measurement which is representative of the total concentration of tars (even as traces) of a hot gas. It involves coupling of methods including one, SPME/GC/MS/PID, which is discontinuous and a priori partial, the other, PID, which is continuous but difficult to interpret alone. It is based on on-line processing of the elements transmitted by each of the measurement methods used. A tar generator ( 28 ) allows calibration of the apparatuses and calculation of the different coefficients required.

1. A device for continuous measurement of the total concentration of tars, which may even be in the form of traces, in a gas characterized in that it comprises:
 a first line for continuous measurement of the total amount of tars, by means of a photo-ionization or flame-ionization detector ( 32 ), 
 a second line for sequential measurement of the total amount of tars successively including means for extracting and concentrating the tars present in the gas ( 12 ,  13 ), means for separating different species of tars concentrated previously ( 25 ), means for identifying the different species of tars separated previously ( 27 ) and a detector identical with the one of the first measurement line ( 26 ), 
 a generator of calibrated tar atmospheres connected to the first measurement line and to the second measurement line, 
 means for processing the measurements ( 36 ) from the first detector ( 32 ) and from the second detector ( 26 ), capable of comparing the data for each of the detectors ( 26 ,  32 ) in order to indicate the total amount of tars measured by means of the first detector from measurements made with the second detector. 
 
     
     
       2. The measurement device according to  claim 1 , characterized in that the means for extracting and concentrating gas samples comprise a solid with reversible absorption or adsorption. 
     
     
       3. The measurement device according to  claim 2 , characterized in that the means for extracting and concentrating samples of the gas comprise a sampling ampoule, a syringe passing through a plug of the ampoule, and in that the solid is a fibre sliding in the syringe. 
     
     
       4. The measurement device according to  claim 3 , characterized in that the fibre is in PDMS (polydimethylsiloxane) or in a carbonaceous compound (of the carbon nanotube or graphitic structure type). 
     
     
       5. The measurement device according to  claim 1 , characterized in that the first detector and the second detector are photo-ionization detectors. 
     
     
       6. The measurement device according to  claim 5 , characterized in that the photo-ionization detectors are adjusted to a value comprised between 10 and 11 eV, preferentially to 10.6 eV. 
     
     
       7. The measurement device according to  claim 1 , characterized in that the means for separating the different species of tars concentrated previously are a chromatograph. 
     
     
       8. The measurement device according to  claim 1 , characterized in that the means for identifying the different species of tars separated previously are a mass spectrometer. 
     
     
       9. The measurement device according to  claim 1 , characterized in that the measurement lines are heat-insulated and maintained at constant temperature. 
     
     
       10. The measurement device according to  claim 1 , characterized in that the generator of tar atmospheres comprises a tank of liquid tars, a device with a gas stream passing through the tank, and a device at the inlet of the tank in order to divide the gas stream into bubbles in the tank. 
     
     
       11. The measurement device according to  claim 1 , characterized in that the first measurement line comprises means for adjusting temperature. 
     
     
       12. The measurement device according to  claim 1 , characterized in that the second measurement line comprises an enclosure ( 11 ) for conditioning the pressurized gas before the means for extracting samples. 
     
     
       13. A method for continuous measurement of the total concentration of tars, which may be even in the form of traces, in a gas, characterized in that it comprises:
 first means for continuous measurement of said total concentration have a first detector ( 32 ) which is a photo-ionization or flame-ionization detector, 
 periodic extractions of samples of gas, every time followed by separation of different species of tars present in said samples, by measurement of the concentrations of said species by a second detector ( 26 ), and by inference of a response coefficient of the first detector ( 32 ) from the concentrations of said species, 
 and continuous estimations of the total concentration of tars by the measurements of the first detector and the response coefficient of the first detector. 
 
     
     
       14. The method for continuous measurement of the total concentration of tars in a gas according to  claim 13 , characterized in that the response coefficient of the first detector is the reciprocal of the sum of the ratios of the concentration and of a particular response coefficient of the first detector, for each of said species. 
     
     
       15. The method for continuous measurement of the total concentration of tars in a gas according to  claim 13 , characterized in that it comprises a selection of the species, only retaining predominant species in the gas. 
     
     
       16. The method for continuous measurement of the total concentration of tars in a gas according to  claim 15 , characterized in that the retained species give a global signal on the second detector having a relationship with a total signal of the sample which is above a threshold. 
     
     
       17. The method for continuous measurement of the total concentration of tars in a gas according to  claim 15 , characterized in that it comprises, for each of the samples, a periodic estimation of the total concentration of tars by the second detector ( 26 ) and a comparison of said periodic estimation with a simultaneous estimation inferred from continuous estimations of the total concentration of tars. 
     
     
       18. The method for continuous measurement of the total concentration of tars in a gas according to  claim 17 , characterized in that it comprises a complement of the selection of retained species if a relative deviation between the periodic estimation and the simultaneous estimation is above a threshold. 
     
     
       19. The method for continuous measurement of the total concentration of tars in a gas according to  claim 17 , characterized in that it comprises a modification of the measurement conditions by the first detector if a relative deviation between the periodic estimation and the simultaneous estimation is above a threshold, the measurement conditions including temperature and pressure. 
     
     
       20. The method for continuous measurement of the total concentration of tars in a gas according to  claim 17 , characterized in that it comprises a modification of the measurement conditions by the first detector if a relative deviation between the periodic estimation and the simultaneous estimation is above a threshold, the measurement conditions including filtering of the gas. 
     
     
       21. The method for continuous measurement of the total concentration of tars in a gas according to  claim 13 , characterized in that the gas is at a temperature comprised between 25° C. and 500° C. 
     
     
       22. The method for continuous measurement of the total concentration of tars in a gas according to  claim 13 , characterized in that the gas is at a pressure comprised between atmospheric pressure and 10 bars.